Accomodating device for retaining wafers

ABSTRACT

A receiving means for receiving and mounting of wafers, comprised of a mounting surface, mounting means for mounting a wafer onto the mounting surface and compensation means for active, locally controllable, compensation of local and/or global distortions of the wafer.

RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.14/693,074, filed Apr. 22, 2015, which is a division of U.S. Ser. No.13/994,183, filed Aug. 9, 2013 (now U.S. Pat. No. 9,312,161, issued Apr.12, 2016), which is a U.S. National Stage Application of InternationalApplication No. PCT/EP2010/007793, filed Dec. 20, 2010, said patentapplications hereby fully incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to a receiving means for receiving and mounting ofwafers and a device and a method for aligning a first wafer with asecond wafer using the receiving means.

BACKGROUND OF THE INVENTION

Receiving means for receiving and mounting of wafers or sample holdersor chucks are available in diverse versions and a flat receiving surfaceor mounting surface is important for the receiving means, so thatstructures, which are becoming smaller and smaller, can be correctlyaligned and bonded on wafer surfaces, which are larger and larger overthe entire wafer surface. This is especially important when a so-calledprebonding step, which joins the wafers to one another by means of aseparable interconnection, is carried out before the actual bondprocess. High alignment accuracy of the wafers to one another isespecially important when an alignment accuracy or especially distortionvalues of <2 μm are to be achieved for all structures located on one orboth wafers. In the vicinity of the alignment marks this succeedsespecially well in the indicated receiving means and devices foralignment, so-called aligners, especially bond aligners. With increasingdistance from the alignment marks, controlled and perfect alignment withalignment accuracies or especially distortion values better than 2 μm,especially better than 1 μm and even more preferably better than 0.25 μmcannot be achieved.

SUMMARY OF THE INVENTION

The present invention provides improved generic receiving means suchthat more accurate alignment can be achieved with them.

This object is achieved with the features of the claims.

Advantageous developments of the invention are given in the dependentclaims. All combinations of at least two of the features given in thespecification, the claims and/or the figures also fall within theframework of the invention. At the given value ranges, values within theindicated limits will also be disclosed as boundary values and will beclaimed in any combination.

The invention is based on the finding of the applicant according toEuropean patent applications EP 09012023 and EP 10 015 569(corresponding to U.S. Patent Application Publication Nos. US2012/0237328 A1 and US 2012/0255365 A1, respectively), with the former adetection of the entire surface, especially the positions of thestructures on the surface of each wafer as a position map of the waferbeing possible. The latter invention relates to a device for determininglocal alignment errors which have occurred due to strain and/ordistortion of the first wafer relative to a second wafer when the firstwafer is joined to the second wafer, with the following:

-   -   a first strain map of strain values along a first contact        surface of the first wafer and/or    -   a second strain map of strain values along a second contact        surface and    -   evaluation means for evaluating the first and/or second strain        maps by which the local alignment errors can be determined. US        2012/0237328 A1 and US 2012/0255365 A1 are hereby incorporated        herein by reference.

At least one strain map of strain values is determined along at leastone of the substrates after joining the substrates, and with thedetermined strain values local alignment errors can be determined. Localalignment errors relate preferably to local structures or groups oflocal structures of the substrates.

A displacement map of the substrate or the two substrates is preparedfor the displacements caused by the joining of the substrates. Thedisplacements are caused especially by distortions and/or strains of thesubstrates.

The seriousness (→distortion vectors) of the distortion introduced bythe pre-bonding step or joining step is estimated, especially at aplurality of local positions on the respective substrate, preferably atpositions dictated by a position map of the respective substrate. Thealignment accuracy which has actually been achieved after thepre-bonding can be measured using the transparent window, but thisindicates, as described below, only little about the actually achievedaccuracy on the entire wafer since it is these distortions which candegrade the result. Since the wafers are not transparent to infraredradiation, the alignment accuracy cannot be directly measured. This isestimated by means of detecting the stress maps and/or the strain maps.

One important aspect is that the apparatus can be provided separatelyfrom the alignment device as an independent module.

The module division can be as follows:

-   -   1) module for detecting a stress and/or strain map before        joining (bonding or pre-bonding)    -   2) alignment module especially according to US 2012/0237328 A1.        But wafer alignment could also take place using only two        alignment marks. In this case the position maps would not be        detected by real measurement, but would be known based on the        wafer layout.    -   3) at least one measurement module for detecting the stress maps        after bonding.

Another application could be conceived in which one of the two wafers islargely unstructured, i.e. has at maximum alignment marks. In this caseit is a matter of being able to estimate distortions of the structuredwafer. In this embodiment there is no “measured” position map, but onlyinformation or data about existing distortions of the exposure fieldsand information on where these exposure fields are located on the wafer.These data are “read in” and would be known on the one hand from thewafer layout (positions). The already existing distortions are measuredwith a measurement device which is suitable for this purpose (generallythe lithography system is used for this purpose).

In this situation the focus can be less on the alignment (exactalignment) (one of the wafers is largely unstructured), but onlydistortions of the structured wafer are relevant. The alignment betweenthe two wafers is either only coarse here (mechanical-edge to edge) oroptical (by means of the alignment marks which are applied to largelyunstructured wafers).

The demands on the optical alignment are however generally rather low.

The position maps are recorded/detected in one advantageous version asin US 2012/0237328 A1 which is described again here.

It describes a method in which the X-Y positions of alignment keys oftwo substrates which are to be aligned can be detected or measured in atleast one X-Y coordinate system which is independent of the movement ofthe substrates so that the alignment keys of a first substrate can bealigned by correlation of the pertinent alignment keys of a secondsubstrate into the corresponding alignment positions. Thus a positionmap of each substrate which is to be aligned is prepared.

In other words: The device makes available means for detecting themovement of the substrates, especially exclusively in an X- andY-direction, which are references to at least one fixed, especiallylocally fixed reference point and thus at least in one X- andY-direction enable an exact alignment of the corresponding alignmentkeys.

The position map can be recorded with the following steps:

-   -   arrangement of the first contact surface in a first X-Y plane        and of the second contact surface in a second X-Y plane which is        parallel to the first X-Y plane,    -   detection of X-Y positions of first alignment keys which are        located along the first contact surface in a first X-Y        coordinate system which is independent of the movement of the        first substrate by first detection means and detection of X-Y        positions of second alignment keys which are located along the        second contact surface and which correspond to the first        alignment keys in a second X-Y coordinate system which is        independent of the movement of the second substrate by second        detection means,    -   alignment of the first contact surface in a first alignment        position which is determined based on the first X-Y positions        and alignment of the second contact surface in a second        alignment position which lies opposite to the first contact        surface and which is determined based on the second X-Y        positions.

This also applies especially to the recording and movement of wafers onthe platforms and the coordinate systems and their relation to oneanother which can also be used for recording/detecting the strain mapsand/or stress maps if nothing to the contrary is described here.

By the combination of positions maps, strain maps and/or stress maps,especially in conjunction with the transparent regions, it is possibleto detect faulty alignment which occurs after or due to contact of thewafers, especially after or during the pre-bonding step and to separatethe wafers from one another again or to separate them from theproduction process.

One problem is that with existing technologies, conventionally only avery highly limited number of alignment marks is detected.Conventionally the alignment is carried out only using 2 alignmentmarks. This can then result in the above described adverse effects thatthe alignment can be good at the locations of the alignment marks and inthe regions directly adjacent to the alignment marks, while thealignment in the remaining regions of the wafer can be inadequate.

Another problem consists in that depending on the selected bond processboth in pre-bonding of the wafers and also in final bonding of thewafers, mechanical distortions can occur on one or two wafers which canlead either locally or even globally to degradation of the alignmentaccuracy. The importance/effect of these distortions with respect tosuccessful alignment of the wafers increases with the required alignmentprecision, especially for required accuracies better than 2 μm. Foralignment accuracies >2 μm these distortions are small enough not torepresent a significant effect on the alignment result.

These distortions constitute a problem not only in the bonding of twostructures substrates, but can also lead to major problems in bonding ofa structured substrate onto a largely unstructured substrate. This isespecially the case if, after bonding, other process steps which requirea very accurate alignment to the structured substrate are to be carriedout. In particular, lithography steps in which additional layers ofstructures are to be aligned to structures already existing on thesubstrate impose high demands here. These demands rise with decreasingstructure size of the structures to be produced. This application arisesfor example in the production of so-called “backside illuminated CMOSimage sensors”. Here a first wafer with the already structured surfaceis bonded onto a carrier wafer which is especially largely unstructured.After forming a permanent bond connection, most of the wafer material ofthe structured wafer is removed so that the structured surface,especially the light-sensitive sites, become accessible from the back.Subsequently this surface must be subjected to other process steps,especially lithography, in order for example to apply the color filterswhich are necessary for operation of the image sensor.

Distortions of these structures adversely affect the alignmentaccuracies which can be achieved in this lithography step. For thecurrent generation of image sensors with a pixel size of for example1.75 μm or 1.1 μm, the distortions allowable for an exposure field (upto 26×32 mm) of a step and repeat exposure system are roughly 100 nm,still better 70 or 50 nm.

Pre-bonding in this document designates bonding connections which afterthe completed pre-bonding step still allow separation of the substrates,especially of the wafers, without irreparable damage of the surfaces.Therefore these bond connections can also be called reversible bonds.This separation is conventionally possible based on the fact that thebond strength/adhesion between the surfaces is still relatively low.This separation is conventionally possible until the bond connection ispermanent, i.e. no longer separable (non-reversible). This is especiallyattainable by the passage of a certain time interval and/or action onthe wafers from the outside by means of physical parameters and/orenergy. Here especially the compression of the wafers by means of acompressive force or the heating of the wafers to a certain temperatureor exposure of the wafers to microwave irradiation are suitable. Oneexample for this pre-bond connection would be a connection between awafer surface with thermally produced oxide and a wafer surface withnative oxide, van-der-Waals connections between the surfaces occurringhere at room temperature. These bond connections can be converted intopermanent bond connections by temperature treatment. Advantageouslythese pre-bonding connections also allow inspection of the bondingresult before forming of the permanent bond connection. In the case ofdeficiencies ascertained in this inspection the substrates can beseparated again and rejoined.

A simple example is a measurement device and measurement method, whichenable detection of the stresses introduced by the pre-bonding step in awafer or a wafer pair. This takes place by means of analysis of thestress maps before and after bonding. A stress difference map isproduced therefrom according to the following description.

The stress difference map enables an especially empirical estimate ofthe distortion/strain introduced by the pre-bonding step. A distortionvector field or a distortion map/strain map is produced therefrom.

This distortion vector field makes it possible for wafer pairs in whichonly one of the two wafers is structured to determine which distortionswere produced at certain positions, especially on the corners of theexposure field, preferably at the positions of the alignment marks forthe lithography device, in addition to the deviations from the idealshape which already exist before bonding.

The distortion vector field alternatively makes it possible, for waferpairs with two structured wafers, to predict which additional alignmentdeviations can be expected at the points detected in the position mapsin addition to the already theoretically expected (as a result of theselected ideal alignment positions based on the position maps of the twowafers) deviation vectors. This yields a deviation vector field or adisplacement map.

This expected deviation vector field can be superimposed or added to thedeviations, which have been determined based on measurements in thetransparent windows. This results then in the alignment result which isto be ultimately expected for all correspondingly provided positions ofthe position map. With this result a decision can be made whether thejoined wafers are to be separated again.

A device and a method can be devised in which

-   -   each alignment position of the two wafers to one another can be        determined, with which the set of all structures on the contact        surfaces of the wafers to one another are economically and/or        technically optimum to one another. This relative position can,        but need not necessarily, correlate with a perfect alignment of        the alignment marks to one another. Of course the alignment        marks are also almost always in the optimum position, i.e. at        least relative to the μm range in the immediate vicinity, but        even not necessarily perfect.    -   for already completed “prebond” process, therefore in a state in        which it is still possible to separate the two wafers from one        another, it can be checked whether the stresses produced in the        pre-bonding step and the distortions which probably derive        therefrom, especially mechanical distortions, are at an        acceptable order of magnitude. This is used especially in        applications in which only one of the two wafers is structured        and the second wafer is largely unstructured.    -   for already completed “prebond” process, therefore in a state in        which it is still possible to separate the two wafers from one        another, it can be checked whether the accuracy of positioning        of the two wafers or of the individual structures of the wafers        to one another also in fact correspond to specifications. In        this way, the displacements which occur as the wafers mutually        approach one another in the direction of the z-axis, or even        worse, deviations from the ideal position which occur during the        contact process, can be determined. In particular, as a result        of detecting the stresses introduced in the pre-bonding step,        predictions of the expected distortions and the resulting        deviations from the ideal position can also be estimated,        especially empirically.

With this device and this method alignment accuracies of <25 μm,especially <0.15 μm, preferably <0.1 μm can be accomplished with goodreliability and yield by the above described distortions beingcontrollable and correctable optionally before producing the final bondconnection.

In other words, the device therefore makes available at least means fordetecting the stress properties of the wafers before and/or after thepre-bonding step. Based on the knowledge of these stress properties andespecially a comparison of the stress properties before and after thepre-bonding step, predictions can be made about strains/distortionswhich have been introduced into the wafer during the pre-bonding step.

Especially for the inspection and/or alignment of two structured wafers,the device can make available means for detecting the movement of thesubstrates, especially solely in one X and Y direction which arereferenced to at least one fixed, especially locally fixed referencepoint and thus enable exact alignment of the corresponding alignmentkeys at least in one X and Y direction, not only with reference to thepositions of the individual structures, but also with respect to thestrain and/or stress properties.

The economically and/or technically optimum alignment of all structuresof the two wafers to one another can be determined, measured and/orchecked. This comprises the recording of a position map of thestructures of the two wafers before the wafers are brought together, anda continuous, especially in-situ monitoring process of the displacementof the two wafers via alignment marks. For faulty prealignment andprebond the generally very expensive structure wafers can be againseparated from one another and re-aligned.

The apparatus can be made to take into account first position maps offirst alignment keys and/or second position maps of second alignmentkeys, especially in the determination by evaluation means. Alignmentkeys are especially the alignment marks and/or structures applied to thesubstrates or one of the substrates.

The stress and/or strain maps are recorded either from the respectiveinspection side by reflection measurement, the radiation beingreflected. In particular an average value of the stress/strain over thelayer thickness is not enabled, but information about regions near thesurface, light infrared or from the respective back by transmissionmeasurement is enabled as claimed in the invention. In measurement withinfrared light or x-ray an average value of the stress or strain overthe detectable layer thickness is determined. A stress-strain map is notnecessarily recorded through the transparent regions. The position mapsare determined especially solely by reflection measurement, preferablyby using visible light. The first and second alignment keys can bedetected at the same time, especially with the same detection means, bythe aforementioned measures.

The alignment of the substrates during contacting and/or bonding of thesubstrates can be checked, especially in-situ. The in-situ checkingentails the advantage that alignment errors caused especially bymovement of the substrates during contact or bonding can be precluded.

To the extent four corresponding alignment keys are provided forchecking, checking taking place especially through transparent regions,simultaneous in-situ monitoring of the relative position of thesubstrates to one another can also take place.

The basic idea of this invention is to provide a receiving meanscomprised of several active control elements which are independent ofone another and with which the mounting surface of the receiving meanscan be influenced, especially in shape and/or temperature. Here, theactive control elements are used by the corresponding activation suchthat the local alignment errors or local distortions which are known bymeans of the position maps and/or strain maps are compensated or for themost part minimized or reduced. Not only are local distortionseliminated, but a macroscopic distortion or stretching of the waferwhich arises from the local distortions altogether in its outsidedimensions is at the same time minimized or corrected.

Thus, as claimed in the invention, especially in combination with theabove described inventions relating to the position maps, strain mapsand/or stress maps and the in-situ correction of alignment faultsdisclosed there during contact-making and bonding of the wafers, it ispossible to achieve a still better alignment result by active,especially local action on distortions of the wafer.

According to one advantageous embodiment of the invention, thetemperature of the mounting surface can be locally influenced by thecompensation means. A local temperature increase of the mounting surfaceleads to local expansion of the wafer which is held on the mountingsurface at this position. The higher the temperature gradient, the morethe wafer expands at this position. Based on the data of the positionmaps and/or strain maps, especially the vector evaluation of thealignment error, especially for each position of the position mapsand/or strain maps, it is possible to act on local wafer distortions orto counteract them in a controlled manner.

In this connection vector evaluation is defined as a vector field withdistortion vectors, which field has been determined especially by meansof one of two versions of the invention described below.

The first version relates to applications in which only one of the twowafers is structured. In this case, it is provided as claimed in theinvention that the deviation of the structures is detected, especiallythe deviation of the geometrical shape from the desired shape. In thiscase, the deviation of the shape of exposure fields, especially exposurefields of a step & repeat exposure device, from the nominally expectedshape which is conventionally rectangular is of special interest. Thesedeviations, especially the vector field which describes thesedeviations, can take place based on the detection of a position map ofthe individual alignment marks which correspond to the exposure fieldsaccording to EP 09012023 (US 2012/0237328 A1). Alternatively, thisvector field can also be determined based on stress maps and/or strainmaps which are acquired by means of EP 10 015 569.6 (US 2012/0255365A1). Advantageously this vector field can however, as claimed in theinvention, also be determined by any other suitable measurement meansand can be read in. In particular, step & repeat lithography systemswhich are operated for acquisition of these data with a special testmask and/or a special test routine are suitable for this measurement.

The second version relates to applications in which two wafers arestructured. In this case, it is provided as claimed in the inventionthat the vector field of the alignment deviation be computed for allpositions of the position maps, especially of the first and secondposition maps according to EP 09012023 (US 2012/0237328 A1). This vectorfield is to be determined especially for the alignment position which isconsidered ideal according to technological and/or economical criteriaaccording to the material in EP 10 015 569.6 (US 2012/0255365 A1).

In another advantageous embodiment of the invention, it is provided thatthe strain of the mounting surface can be locally influenced by thecompensation means, especially by arrangement of piezoelements which canpreferably be individually activated on one back of the mountingsurface. By stretching or shrinkage, therefore negative stretching, themounting surface, also the wafer, is deformed accordingly, especiallystretched or shrunk, especially by the mounting force acting from themounting surface on the wafer, wherein the wafer can be influenced in acontrolled manner by a corresponding control means based on the valuesof the strain map which has been determined for this wafer. To theextent the shape of the mounting surface can be locally influenced bythe compensation means, especially by preferably mechanical action inone Z direction, there is another possibility for counteractingdistortions of the wafer on the mounting surface. Here it also appliesthat the control of the compensation means takes place by a controlmeans which undertakes a correspondingly dedicated local control of thecompensation means based on the values of the position maps and/orstrain maps.

The control means encompasses especially software forexecuting/computing corresponding routines.

According to another advantageous embodiment of the invention, it isprovided that the mounting surface can be locally exposed to pressurefrom the back of the mounting surface, by the compensation means,especially hydraulically and/or pneumatically. In this way the shape ofthe mounting surface can likewise be influenced so that theaforementioned effects occur. Control likewise takes place again by theabove described control means.

Advantageously the compensation means are provided as a plurality ofactive control elements in the receiving means, especially integrated,preferably embedded into the mounting surface. Thus a receiver of thereceiving means can be made monolithic, as is likewise the case in theknown receiving means.

Here it is especially advantageous if each control element or groups ofcontrol elements can be activated separately. Accordingly, localactivation means that a small extract, especially an extract smallerthan half the wafer, preferably smaller than ¼ of the wafer, preferablysmaller than ⅛ of the wafer, even more preferably smaller than 1/16 ofthe wafer, can be locally activated by the compensation means. It isespecially advantageous if the compensation means can act on each regionof the wafer occupied by its own structure with at least one controlelement.

The device as claimed in the invention comprises the above describedcontrol means advantageously in a central control unit which isresponsible for all control processes. But, as claimed in the invention,it is conceivable to provide the control means in the receiving means,especially as a module of an overall device.

The method as claimed in the invention can be still further improved bythere being one, especially repeated, acquisition of position mapsand/or strain maps of the first and/or second wafer after the alignment.Thus, as claimed in the invention after completed alignment, there canbe checking of the alignment success. Accordingly, it is conceivable toeliminate a wafer pair with overly large alignment errors in order, forexample, to align them again as claimed in the invention or to disposeof them. At the same time the acquired data can be used forself-calibration of the device, especially by the control means.

The inventions disclosed in European patent application EP 09012023.9(US 2012/0237328 A1) and/or the European patent application EP 10 015569.6 (US 2012/0255365 A1) will be considered as concomitantly disclosedat the same time as embodiments for this invention.

Other advantages, features and details of the invention will becomeapparent from the following description of preferred exemplaryembodiments and using the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1a shows a plan view of a receiving means as claimed in theinvention in a first embodiment,

FIG. 1b shows a cross sectional view of the receiving means according tocutting line A-A from FIG. 1 a,

FIG. 2a shows a plan view of a receiving means as claimed in theinvention in a second embodiment,

FIG. 2b shows a cross sectional view of the receiving means according tocutting line B-B from FIG. 2 a,

FIG. 3a shows a plan view of a receiving means as claimed in theinvention in a third embodiment,

FIG. 3b shows a cross sectional view of the receiving means according tocutting line C-C from FIG. 3 a,

FIG. 4a shows a plan view of a receiving means as claimed in theinvention in a fourth embodiment,

FIG. 4b shows a cross sectional view of the receiving means according tocutting line D-D from FIG. 4 a.

FIG. 5a shows a schematic cross sectional view of a wafer pair which hasbeen aligned as claimed in the invention,

FIG. 5b shows a schematic aspect of an upper wafer of the wafer pairaccording to FIG. 5 a,

FIG. 5c shows a schematic aspect of a lower wafer of the wafer pairaccording to FIG. 5 a,

FIG. 6a shows a schematic view of the process step of detecting a firstwafer as claimed in the invention,

FIG. 6b shows a schematic view of the process step of detecting a secondwafer as claimed in the invention,

FIG. 6c shows a schematic view of the in-situ detection of the alignmentof the wafers as claimed in the invention when the wafers make contact,

FIG. 7 shows an enlargement of one alignment mark for a perfectlyaligned and contacted wafer pair,

FIG. 8 shows an enlargement of one alignment mark for an imperfectlyaligned and contacted wafer pair with an enlargement of corners of twostructures of the wafer pair which are to be aligned to one another,

FIGS. 9a to 9c show one alternative method for detecting the alignmentof a wafer pair and

FIG. 10 shows a schematic of the determination of a displacement map asclaimed in the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The same components/features and components/features with the sameaction are identified with the same reference numbers in the figures.

FIG. 5a shows a typical wafer system consisting of a first substrate 10,especially a wafer 10, with a surface 10 o, and a second substrate 20,especially a wafer, with a surface 20 o. On the surfaces 10 o, 20 o aredifferent structures 50, 50′ which are to be bonded to the contactsurfaces 10 k, 20 k. The structures 50, 50′ can be for example cavitiesin which there are MEMS devices. In the case of 3D integrated chipstacks the structures could also be metal surfaces which are used forproducing electrical connections. For the sake of simplicity thestructures 50, 50′ are shown as black rectangles. FIGS. 5b and 5c showthe surfaces 10 o, 20 o of the two wafers 10, 20. The wafer 20 has fourregions 400 with second alignment keys 40.1 to 40.4.

The regions 400 are transparent to electromagnetic radiation of acertain wavelength or a certain wavelength range. A first detectionmeans 70, especially optics, can correlate the first alignment keys 30.1to 30.4 of the first wafer 10 with the corresponding second alignmentkeys 40.1 to 40.4 through the transparent regions 400. Advantageouslythese transparent regions can be made available for silicon wafers bydoping of the silicon being avoided for these regions or especially thedegree of doping being kept relatively low and no metal layers beingapplied in these regions or especially relatively few metal structuresbeing produced. This can be achieved for example in that only thealignment marks and possible pertinent structures which can consistespecially of metal are placed in the transparent regions. Withadherence to these prerequisites silicon is transparent to infraredlight with a wavelength of >1 μm, especially >1050 nm.

The structures 50, 50′ can project over the surfaces 10 o, 20 o or canbe set back relative to them, for which reason the contact surfaces 10k, 20 k need not coincide with the surfaces 10 o, 20 o of the wafers 10,20.

Alignment keys 30.1 to 30.n or 40.1 to 40.n can be also be thestructures 50, 50′ or parts of the structures 50, 50′.

The method begins with the recording of the position maps. A positionmap is defined as the position detection, spatially as complete aspossible, of as many structural elements as possible, especially of thefirst and/or second alignment keys 30.1 to 30.n or 40.1 to 40.n and/orstructures 50, 50′ or parts of the structures 50, 50′ on the surface ofthe wafers 10, 20.

FIG. 6a shows the position detection of the surface 10 o of the firstwafer 10 by the optics 70, therefore the recording of a first positionmap. Positions of the first alignment keys 30.1 to 30.4 are measured onthe top 10 o of the wafer 10 by either the wafer 10 being moved relativeto the optics 70 or the optics 70 being moved relative to the wafer 10.In one preferred embodiment the optics 70 are fixed, while the wafer 10is moved relative to the optics 70, fixed on the recording means 12.

In a second step which especially follows the first step or whichproceeds simultaneously with it, according to FIG. 6b the same processis carried out with the top 20 o of the second wafer 20 by means of asecond detection means, especially optics 80.

Since in this measurement process the recording of the position map iswhat is important, it would also be conceivable to use only the optics70 as the detection means, therefore to omit the optics 80, and tomeasure the two wafers 10, 20 with their structured tops 10 o, 20 o inthe direction of the optics 70. For later alignment and bond step thenone of the two wafers 10, 20 would be flipped and fixed on its recordingmeans 12 or 22.

According to the above described steps, the device now knows the X-Ypositions of all recorded structures 50, 50′ or recorded first andsecond alignment keys 30.1 to 30.n and 40.1 to 40.n on the tops 10 o, 20o of the wafers 10, 20, especially also the positions of the structures50, 50′ relative to the first and second alignment keys 30.1 to 30.n and40.1 to 40.n. They are stored in the form of a first position map forthe first substrate 10 and in the form of a second position map for thesecond substrate 20.

During the measurement step, not only the first and second position map,but especially in different modules or at the same time in one module,also first and second initial strain and/or first and second initialstress maps will be recorded and are representative of the basicstresses or initial stresses of the substrates 10, 20. Here it is therecording of strain and/or stress values as a function of the X-Yposition according to the position map. Each measurement device which isable to determine stresses and/or strains locally resolved, can be used,especially infrared measuring devices. Measurement devices which arebased on Raman spectroscopy are especially advantageously used.Alternatively as claimed in the invention the infrared method“Grey-Field Polariscope” Review of Scientific Instruments 76, 045108(2005) “Infrared grey-field polariscope: A tool for rapid stressanalysis in microelectronic materials and devices” can be used. Thestress and/or strain maps are recorded in turn by relative motion of theoptics 70, 80 to the wafers 10, 20. In one advantageous embodiment thereis separate optics or optics additionally integrated in the optics 70,80.

To the extent only strain maps or only stress maps are prepared foroptimization of the detection time, the stress map can be converted intothe corresponding strain map by means of the fundamental equations ofelasticity theory and vice versa. A mathematical, especially numericconversion, preferably with starting points according to the method offinite elements is conceivable.

For devices which have been optimized for the especially precisedetection of the position maps and/or strain maps, two differentdetection means are used for detection of the position maps and/orstress maps.

For exclusion of other fault sources it is provided that the stressand/or strain maps are detected according to the alignment of thesubstrates 10, 20.

The respective detection means for recording the position maps in oneadvantageous configuration at the same time comprise the detection meansfor detection of the stress and/or strain maps so that movement of therespective detection means with the same drive takes place.

Alternatively, for the accelerated and in this respect more costfavorable embodiment it is conceivable to provide detection of thestress and/or strain maps in one or more separate modules, especiallywith respectively separate wafer handling means, preferably robot arms.

FIG. 7 shows perfectly aligned first and second alignment keys 30.1 to40.1, as well as perfectly aligned structures 50, 50′, the structure 50′being covered by the structure 50 due to the perfect overlapping. Thecase is unrealistic in which all structures 50, 50′ on the two wafers10, 20 with reference to the alignment keys 30.1 to 30.n and 40.1 to40.n have been produced so perfectly that in a perfect bond process thestate from FIG. 7 results. In actuality the structures 50, 50′ cannot beso exactly produced. Even if they were so perfectly produced, the wafers10, 20 during the approach process or while “coming into contact” couldmove relative to one another. In the pre-bonding step additional strainscan also be introduced into the wafer which lead to strain/distortionsand as a further consequence to deviations from the ideal alignment. Aperfect alignment at individual positions is accordingly not necessarilythe objective. Rather, care should be taken that all correspondingstructures 50, 50′ on the wafers 10, 20 are aligned altogether withregard to economic and/or technical aspects such that for each waferpair which is to be bonded and aligned dice scrap is as little aspossible.

Since the positions of all detected structures 50, 50′ and/or of thefirst and second alignment keys 30.1 to 30.4 and 40.1 to 40.4 of the twowafers 10, 20 are known, the optimum relative position of the wafers 10,20 or of all structures 50, 50′ to one another can be determined bycomputation means. This takes place by determining a first alignmentposition of the first contact surface 10 k and a second alignmentposition of the second contact surface 20 k based on the values of thefirst position map and based on the values of the second position map.This relative position of the wafers 10, 20 to one another and/or thefirst and second alignment position can be continuously checked in-situfor correctness during and also after contacting and during as well asafter the bonding process by the optics 70 and through the transparencyregions 400. In this way the alignment can be checked in-situ.

The optimum relative position of the two wafers 10, 20 or of thestructures 50, 50′ to one another arises for example by computing aminimum sum of the especially quadratic deviations of the respectivelycorresponding structures 50, 50′ from one another.

It is likewise conceivable to allow economic aspects to also be includedin this computation of the ideal alignment position. Thus, in many areasof the semiconductor industry, especially in the memory industry (forexample, RAM, NAND Flash) it is conventional that chips on certainregions within the wafer, especially in the region of the wafer center,have less variance of the quality-relevant parameters. Therefore thechips which originate from this region attain higher sales prices sothat the sorting process in which these chips are intentionally dividedinto different quality baskets is taken into account (this process isknown as “binning”). Advantageously therefore as claimed in theinvention the ideal alignment position of the wafers is computed notonly based on the position maps of the two wafers, but an economiccomputation/weighting is also included here, in which especially care istaken to achieve a higher yield in the area of the higher quality chips,especially at the cost of a lower yield in the region of the lower valuechips.

FIGS. 8 and 10 show a difference vector u which constitutes thedifference of the X-Y positions of the corners of an upper structure 50from those of a corresponding lower structure 50′. The difference vectoru arises for example from the minimization computation of the positionmaps. Of course in each of the transparent regions 400 its owndifference vector u can be recognized. If at this point the two wafersapproach one another, the difference vectors u are continuously checked.If they change, during the approach or during contacting or bonding, adeviation from the determined relative position of the two wafers 10, 20to one another takes place. Even if the two wafers 10, 20 make contact,the optics 70 can still check at least the four difference vectors uthrough the transparency regions 400. If after contact a deviationshould be effected which is too large, the wafers 10, 20 are immediatelyseparated in order to carry out alignment and the prebond process again.In order to implement a simultaneous checking of several transparencyregions 400, for each transparency region 400 there is its own optics 70so that the throughput during bonding is not reduced by the in-situdetection of the alignment.

Alternatively it is also conceivable to carry out the checking stepafter pre-bonding in a separate module, so that the throughput of thealignment means and of the pre-bonding module is not reduced. Thepossible separation of the wafers after the checking step can take placeeither in the module intended for checking or however likewise in aseparate module. It is also conceivable that not all modules areconnected in a single device, but form separate devices, especially withwafer handling means which are separate at the time.

FIG. 7 shows in an enlargement the near region of the alignment marks30.1 and 40.1. In order to be able to detect the structures 50 and 50′during superposition, only the edges have been shown. If at this pointthe structures 50 and 50′ were oriented perfectly to one another, andperfectly to the alignment marks 30.1 and 40.1, a perfect covering ofthe two structures 50 and 50′ would be established in a bond process.

FIG. 8 shows the sample case in which there is no coverage of thestructures 50 and 50′, although the alignment marks 30.1 and 40.1 havebeen perfectly aligned to one another. In the enlargement of thestructure 50 and the corresponding structure 50′ it is recognizable thatthe difference vector u has one X- and one Y-component which can be usedfor vector computation.

The aforementioned measurement instruments or measurement instrumentsprovided in a separate module can be used for stress and/or strainmeasurement after prebonding or bonding in order to determine the stressand/or strain maps of the bonded wafer stack. By measuring the initialstress and/or initial strain maps of the wafers 10, 20 before bonding ofthe two wafers 10, 20 to the wafer stack and the measuring the stressand/or strain maps of the wafer stack, conclusions can be drawn aboutthe deformation at the instant of contact or shortly afterwards can bedrawn. In other words, therefore the stress introduced by thepre-bonding process can be measured and the resulting stress/distortioncan be determined/estimated/predicted or advantageously computed,especially based on empirically determined relationships.

Although the inner regions of the wafers 10, 20 can no longer be viewedwith the optics 70, 80, since there are no transparent regions in thisregion, conclusions can be drawn about the state, the position or thedeformation in this region by the strain and/or stress maps. If forexample in one region a stress prevails which exceeds a critical value,for example the value of a comparison stress, this region can beautomatically marked as a problem zone by software. The dices could thusbe divided into quality classes. Dices with low inherent stresses have agood quality class as well as long service life, while dices with highstress concentration can be classified into a low quality class.

Based on these stress/strain maps, for the entire wafer surface and allstructures present on it the alignment accuracy which has been achievedis estimated and empirically determined. This can be done as follows inpractice.

1) Detecting the first and second position maps, corresponding to thefirst and second wafers as described above.

2) Computing the ideal alignment position based on this first and secondposition map according to technical and/or economic criteria. Thiscomputation likewise yields the ideal alignment positions and thecorresponding deviation vectors for the alignment marks in thetransparent regions 400. That is, the alignment marks in the transparentregions 400 need not necessarily be perfectly aligned in order toachieve the optimum result viewed for the entire wafer. Furthermore,based on this computed desired alignment position a two-dimensionaldifference vector field v′ which can be expected for this reason (seeFIG. 10) with individual difference vectors for at least the predominantnumber, preferably all positions contained in the position maps, iscomputed. Here preferably sites at which there are no structures 50, 50′are left out in order not to adulterate the measurement result. They arefor example the locations of the alignment keys 30.1 to 30.4 and 40.1 to40.4 since there are alignment marks there instead of structures 50,50′.

3) Detecting the first and second initial stress map corresponding tothe first and second wafer before the pre-bonding step, especiallyparallel to detection of the first and second position map.

4) Pre-bonding of wafers with a suitable method. These methods are knownin basic form to one skilled in the art for the most varied bondingconnections.

5) Detecting the actual alignment accuracy in the transparent regions400 and determining the actual deviation vectors u in the transparentregions 400.

6) Determining the difference between the actual deviation vectors ufrom the computed deviation vectors for the transparent regions.

7) With consideration of the determined difference the resultingdifference vector map v″ can be computed in which for at least thepredominant number, especially for each position contained in the firstand second position map, there is a deviation vector. These deviationvectors u which correspond to the individual position are now adapted bya correction vector which is computed for each individual position basedon the deviation vectors determined under item 60 and the coordinateposition of the respective point and the coordinate positions of thetransparency fields.

8) Detecting the first and second stress map after pre-bonding.

9) Comparing the first stress map before and after the pre-bonding andthe second stress map before and after the pre-bonding.

10) Predicting the additional alignment errors/deviation vectors whichcan be expected for individual points based on the stress differencesbefore and after the pre-bonding.

11) Adding the additional deviation vectors caused by the stressintroduced in the pre-bonding to the deviation vectors which can betheoretically expected and which were computed in point 7.

12) Deciding whether the alignment accuracy to be expected here in thevector field predicted based on the computation in point 11 for thedeviation vectors in the individual points corresponds as before totechnological and economic success criteria or whetherreprocessing/separation of the wafers is to be carried out.

For wafer stacks in which one or both wafers before pre-bonding haveonly low or especially no initial stresses or for which the initialstress before bonding is known because it is subject for example to onlyvery low variance in mass production, on step 3, the detection of stressmaps before bonding for purposes of optimization of the throughput andthe costs can be omitted. It is also possible, especially in the case ofstresses which are subject to only a low variance to subject only onepart of the wafer to detection of the stress maps before bonding. Inthis connection, low stresses are defined as stress values which areinsignificant compared to the stresses produced in the pre-bonding step.This is especially the case when the stresses differ by the factor 3,preferably by the factor 5 or even better by the factor 10. With respectto only partial measurement of the wafer stack it is especially feasiblefor example to subject the first and the last wafer stack of a batch toinspection and for the remaining wafer stacks to adopt the stress mapdetermined for the first wafer stack for the computations. It is alsoconceivable to carry out the computations offset in time in order tothen base the computation on the averaged stress maps for example forthe first and last wafer stack. In this case it is also advantageouslypossible to additionally inspect other wafer stacks in order to achievehigher reliability in the computation of the average value. According tothe described procedure it is also possible to subject only one of thetwo wafers which form the wafer stack to detection of the stress maps.This is especially advantageous when only one of the two wafers does notmeet the above described criteria which justify the omission of stressmap detection.

For applications in which only one of the two wafers is structured themethod can proceed similarly to bonding of two structured wafers.Specifically the process is as follows in this embodiment:

-   -   1) Detecting the already existing distortion/deviation vectors        of the individual exposure fields located on the structured        wafer from the ideal shape by suitable detection means. In        particular step and repeat exposure system which are also        intended for later processing of the bonded wafer enable this        measurement with the aid of suitable devices such as test masks.        This deviation from the ideal shape is represented in the form        of a vector field and is stored for further computation. In        particular this vector field contains vectors for a major part,        especially all positions of the alignment marks, which are        conventionally located on the corners of the exposure fields.    -   2) Detecting the initial stress map of the structured wafer        before the pre-bonding process by suitable detection means from        the side opposite the contact surface 10 k (if wafer 10 is the        structured wafer) or 20 k (if wafer 20 is the structure wafer).    -   3) Alignment of the two wafers to one another with the aid of        suitable detection means for the wafer position and alignment        means.    -   4) Pre-bonding of the two wafers.    -   5) Detecting the stress map of the structured wafer after the        pre-bonding step by means of suitable detection means from the        side opposite the contact surface 10 k/20 k.    -   6) Determining the difference between the stress map before the        pre-bonding step and after the pre-bonding step.    -   7) Deriving the distortion vectors to be expected/the distortion        vector field to be expected based on the stress difference        determined in point 6. Advantageously the vectors in this vector        field are determined for positions which correlate with the        positions of the vectors from the vector field which has been        determined in point 1, especially at least largely agree.        Advantageously this agreement is better than 500 μm, but more        ideally better than 200 or 70 μm.    -   8) Adding the distortion vector field with the vector field        determined in point 1.    -   9) Checking whether the vector field resulting from the        computation in point 8 corresponds as before to technological        and economic success criteria or whether separation and        reprocessing of the wafers are to take place.

The aforementioned statements with respect to omitting the detection ofstress maps before bonding or the only partial detection of the stressmaps for selected wafers and/or wafer stacks apply analogously here.

Deriving the distortion vector field from the stress maps and especiallythe maps for the stress difference between, prior to and afterpre-bonding can take place as claimed in the invention based on aplurality of suitable methods. It is apparent from the detection ofstress maps and especially the stress difference beforehand/afterwardswhether in certain regions of the wafer a pressure or tensile stressduring bonding has been additionally produced. On this basis conclusionscan be drawn about the direction of the individual vectors at any pointof the wafer. The level of the stress difference in the individualregions which is likewise known from the measurements and/or thecomputation allows conclusions about the amount of the vector. Theserelationships are however not necessarily linear since the individualcomponent regions of the wafer are conventionally surrounded by otherregions which additionally influence the strain/distortion of the wafer.Therefore complete computation models which are suitable in practicemust be used to be able to estimate the actual amounts and directions ofthe vectors. Another possibility for certain outline conditions (certainstress values, etc.) is also the use of empirical methods in which thefindings from tests done in the past are exploited.

Without transparent regions 400 the in-situ measurement of the alignmentduring contacting and/or bonding is limited to the measurement of thestrain and/or stress fields, as is shown in FIGS. 9a to 9c . Theexamples of FIGS. 9a to 9c show a method and a device in which insteadof two wafers 10, 20 which are both completely structured, one structurewafer 20′ is aligned relative to a carrier wafer 10′.

The alignment marks 30.1 to 30.n are correlated with the alignment marks40.1 to 40.n by already known optical systems being used. The optics 70and/or 80, if they have the corresponding sensor means which werementioned above, can be used for measurement of the strain and/or stressfields. The stress and/or strain field on the top 20 o of the wafer 20can be measured either by the optics 80 while the carrier wafer 10 hasbeen removed from the visual region (FIG. 9b ) or by the optics 70, ifthe electromagnetic radiation used can penetrate the structure wafer20′. It must be considered by the computation means that in thetransmission measurement by the optics 70 an averaged strain and/orstress value can be obtained if the stress along the layer thicknesschanges (so-called stress gradients in the layer thickness). For themeasurement of the strain and/or stress fields on the surface 10 o ofthe carrier wafer 10′, the above described applies, the necessarychanges having been made, according to FIG. 9 c.

After the respective initial strain and/or stress fields have beenmeasured, the two wafers 10′, 20′ can be aligned and bonded. After thebond is completed, the strain and/or stress fields are determined bymeans of the optics 70 and/or 80. After bonding, only one moretransmission measurement of the strain and/or stress fields of thesurfaces 10 o, 20 o is possible since the electromagnetic radiation mustpenetrate the two wafers 10′, 20′. Therefore the aforementioneddifferentiation between transmission and reflection measurement ispreferred. For better comparability, the transmission measurement ispreferred. If transmission measurements and reflection measurementsshould yield similar strain and/or stress maps, it can be concluded thatthe strain and/or stress fields are only on the surfaces 10 o, 20 o andthere are no stress gradients over the thickness. Thebeforehand/afterwards comparison then in turn allows a conclusion aboutthe change of the strain and/or stress fields and a conclusion aboutpossible weaknesses of the system. If extreme strain and/or stressregions or those exceeding a comparison value are discovered, the wafersystem can again be broken down into the individual wafers before theyare permanently bonded to one another.

For structured wafers which are not transparent to the electromagneticwaves used to detect the stress maps, a reflection measurement can bepreferred since thus the transparency of the structured surface of thewafer, especially the contact surface 10 k or 20 k, does not play apart. For these wafers with the absence of transparency the stress canalso be advantageously measured on the surfaces opposite the surfaces 10o and 20 o. In order to achieve better comparability of the measurementresults, it is a good idea to measure both before and after thepre-bonding and/or the bonding step on these surfaces. Since the stressfields in the wafer viewed in the lateral direction compared to thewafer thickness have a must larger extension, this version of themeasurement also yields very good results. In particular, thecircumstance that lateral stress fields with a certain minimum extensionare needed to cause significant distortions benefits the accuracy. Itcan be expected that stress fields in the lateral direction (X/Y) musthave at least 3 to 5 times, probably even 10, 15 or 20 times theextension relative to the wafer thickness to lead to relevantstrains/distortions.

The most important wafer material combinations which can be used are:Cu—Cu, Au—Au, hybrid bonds, Si, Ge, InP, InAs, GaAs; and combinations ofthese materials and the respectively assignable oxides for materialswhich allow this.

The position, strain and stress maps all relate advantageously to thesame X-Y coordinate system. Thus the vector computation is simplified,especially in the determination of the first and second alignmentpositions and the determination of the displacement map according toFIG. 10.

All four embodiments in FIGS. 1a-4b show a monolithic receiver 1 which,as a flat, preferably circular ring-shaped plate, is provided with aflat mounting surface 1 o for receiving and mounting of wafers. On theouter periphery the receiver has a ring-shaped shoulder 1 a.

The mounting surface 1 o forms a receiving plane for receiving thewafer, which plane extends in the X and Y direction. The Z direction, inwhich the mounting force acting on the water is pointed, runsperpendicular to them. Mounting of the wafer takes place throughopenings 2 which are arranged uniformly distributed in a plurality overthe mounting surface 10 in order to be able to hold the wafer on themounting surface 1 o by applying negative pressure to the openings 2.The larger the number of openings 2 and the smaller the diameter of theopenings 2, the less the negative pressure prevailing on the openings 2for mounting of the wafer leads to distortions of the wafer on theopenings 2.

The negative pressure on the openings 2 is applied via a vacuum meanswhich is not shown and which applies negative pressure to an interiorspace 1 i located on the back side of the mounting surface 1 o. Theinterior space 1 i is furthermore bordered by a peripheral wall 1 w ofthe receiver 1 and is sealed relative to the vicinity. The openings 2extend from the mounting surface 1 o as far as the interior space 1 iand can thus be uniformly exposed to the negative pressure prevailing inthe interior space 1 i.

The interior space 1 i is furthermore bordered by the back 1 r locatedopposite the mounting surface 1 o and by the bottom of the interiorspace 1 i which is not shown, the back 1 r being penetrated by openings2.

On the back 1 r the active control elements are a plurality ofheating/cooling elements, especially exclusively heating elements 3. Theheating elements 3 are each activated individually or in groups, controltaking place by a control means which is not shown. When one of theheating elements 3 is heated, a local section of the mounting surface 1o is heated by the material with very good heat conduction, especiallymetal, of the receiver. This leads to local expansion of a wafer whichlies on the mounting surface 1 o in this region. Thus, for wafers whichare held aligned accordingly on the receiving means and with a knownposition of possible distortions/strains, a deformation of the wafer canbe caused in a controlled manner by switching individual or severalheating elements 3 in order to compensate for local distortions.Especially for a plurality of local compensations, this also yieldsglobal compensation of global distortions, especially a change of thediameter of the wafer in the X and/or Y direction.

One special advantage of influencing the distortions on the wafer bymeans of the heating and/or cooling elements lies in the possibility ofbeing able to achieve this with minimum deformation, especially withoutdeformation of the mounting surface and/or especially withoutdeformation of the wafer in the vertical direction or Z direction. Inthis connection, minimum deformation should be considered to bedeformation of the mounting surface and especially of the wafer in thevertical direction or in the Z-direction relative to the support surfaceof <5 μm, advantageously <2 μm, preferably <1 μm and even morepreferably <0.5 μm.

This is especially advantageous for production of prebondinginterconnections, for example for prebonds, which are based onvan-der-Waals bonds. Based on the fact that here the mounting surfaceand especially the wafer can be kept flat, the bond wave which isconventional in these prebonding steps is not influenced in itspropagation by unevenness. Thus the risk that unbonded sites (so-calledvoids) remain is greatly reduced. For producing these prebondinginterconnections, as claimed in the invention evenness of the mountingsurface of <5 μm, advantageously <2 μm, preferably <1 μm and even morepreferably <0.5 μm over the entire wafer surface is desired. Theseevenness values are defined as the distance between the highest and thelowest point within that part of the mounting surface which is incontact with the wafer.

The heating elements 3 are advantageously uniformly distributed underthe mounting surface 1 o. Advantageously there are more than 10 heatingelements 3, especially more than 50 heating elements 3, preferably morethan 100 heating elements 3, even more preferably more than 500 heatingelements 3, in the receiving means. These heating elements form regionswhich can be separately activated in the mounting surface and whichenable local action on the wafer. Advantageously the individual regionsof the mounting surface are thermally insulated from one another withsuitable means. In particular, the regions are made in a form whichenables a uniform and closed arrangement of the individual segments.Advantageously the execution of the segments as triangles, squares orhexagons is suitable for this purpose.

In particular, Peltier elements are suitable as heating elements 3.

In the second embodiment shown in FIGS. 2a and 2b , heating elements 3are not shown. I Instead of heating elements 3, or in combination withthem, there are piezoelements 4 on the mounting surface 1 o, preferablywith a greater distance to the back 1 r than to the mounting surface 1o.

In this way, a controlled action on the mounting surface 1 o ispossible. The piezoelements 4 can cause strains in the nanometer tomicron range upon activation.

The number of piezoelements 4 can correspond to the aforementionednumber of heating elements 3, a combination of the two embodiments beingconceivable as claimed in the invention.

In the third embodiment of the invention shown in FIGS. 3a and 3b ,instead of or in combination with the heating elements 3 and/or thepiezoelements 4, there are pins 5 which end on the mounting surface 1 owith an especially pointed pin end 5 e. In the initial position of thepins 5 the pin end 5 e is flush with the mounting surface 1 o. To theextent there is a local distortion of a wafer in the region of a certainpin 5 as information of the distortion map or strain map, the controlmeans can act locally on the wafer by activating individual or severalpins 5 by or near the pin 5 or the pin end 5 e being moved in the Zdirection in the direction of the wafer. The pin end 5 e thus locallyexposes the wafer to a compressive force which provides for a localbulging or deflection of the wafer at this point. The pin 5 can beguided to slide as a whole in a guide opening 7 which extends from themounting surface 1 o as far as the back 1 r. Alternatively, only the pinend 5 e can be moved in the pin 5 and the pin 5 or the lower section ofthe pin is fixed relative to the guide opening 7. In this way specialsealing of the pin 5 or of the pins 5 can be ensured relative to theinterior space 1 r.

The number of pins 5 corresponds to the number of piezoelements 4 orheating elements 3, here a combination with one or more of theaforementioned embodiments being possible.

In the embodiment shown in FIG. 4, the receiver 1 has a plurality ofpressure chambers 6, each having an upper wall 6 o (shown in FIG. 4b )that together form the mounting surface 1 o. The pressure chambers 6extend through the interior space 1 i and are sealed relative to this.Each of the pressure chambers 6 or groups of pressure chambers 6 can beseparately pressurized, and control by the described control means cantake place. The pressure chamber 6 is made, at least on its upper wall 6o, such that it yields when pressure is applied. Therefore the upperwall 60 is made either thinner and/or softer than the other boundarywalls of the pressure chambers 6. The openings 2 are connected to theinterior space 1 i.

As claimed in the invention a simply minimum local deflection of themounting surface 1 o takes place by the aforementioned compensationmeans 3, 4, 5, 6 by a maximum 3 μm, especially a maximum 1 μm,preferably a maximum 100 nm.

In order to be able to counteract the local distortions with one or moreof the aforementioned embodiments, as described above it is necessarythat the control means knows where and to what extent or in whatdirection there are distortions in the wafer. Only then is controlledaction or counteraction and compensation of distortions possible. Thestrain map of each wafer yields information in the form of strainvectors which are distributed over the wafer and which have beendetermined with a corresponding measurement means according to EP 10 015569.6 (US 2012/0255365 A1). Corresponding control data can be filed inthe control unit, especially empirically determined, in order to be ableto undertake for each wafer an individual control according to thestrain map of the wafer at the positions dictated by the position map ofthe wafer. Compensation can be carried out automatically in this wayduring alignment of the wafers.

The active control elements 3, 4, 5, 6 are shown not to scale in thefigures and can also have different sizes and shapes.

Having described the invention, the following is claimed:
 1. A methodfor alignment of a first wafer with a second wafer, comprising:determining local alignment errors that have occurred due to strainand/or distortion of the first wafer relative to the second wafer whenthe first wafer is joined to the second wafer; receiving one or more ofthe first and second wafers on a mounting surface of a plate, thereceiving comprising: mounting the wafers on the mounting surface byholding the wafers on the mounting surface through application ofnegative pressure to openings formed through the mounting surface; andactively, at least partially, compensating respective global distortionsof the wafers through a plurality of piezoelements integrated into themounting surface, the piezoelements being on the mounting surface andconfigured to cause strain on the mounting surface; and aligning thefirst and second wafers with each other based on the determined localalignment errors with the compensation by the piezoelements, wherein thecompensating takes place simultaneously during the aligning.